<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>天气案例_监视属性</title>
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
    <div id="root">
        <h2>今天天气很{{info}}</h2>
        <button @click="changeMeather">切换天气</button>
    </div>
</body>
<script type="text/javascript">
    Vue.config.productionTip=false;
    const vm=new Vue({
        el:'#root',
        data:{
            isHot:true
        },computed: {
            info(){
               return this.isHot?'炎热':'凉爽'
            }
        },
        methods: {
            changeMeather(){
                this.isHot=!this.isHot
            }
        },
        // watch:{
        //     isHot:{
        //         immediate:true, //初始化时让handler调用一下
        //         //handler调用：当isHot发生改变时
        //         handler(newValue,oldValue){
        //             console.log('isHot被修改了',newValue,oldValue)
        //         }
        //     }
        // }
    })
    vm.$watch('isHot',{
        immediate:true, //初始化时让handler调用一下
        //handler调用：当isHot发生改变时
        handler(newValue,oldValue){
        console.log('isHot被修改了',newValue,oldValue)
      }
    })
</script>
</html>